Thanks again Petr, for the deep analysis! Much appreciated. Some comments inline below: On 19/01/2022 12:48, Petr Mladek wrote: >[...] > From my POV, the function of panic notifiers is not well defined. They > do various things, for example: > [...] > > The do more that just providing information. Some are risky. It is not > easy to disable a particular one. We are trying to change that here: https://lore.kernel.org/lkml/20220108153451.195121-1-gpiccoli@xxxxxxxxxx/ Your review/comments are very welcome =) > [...] > It might make sense to allow to call kmsg_dump before panic notifiers > to reduce the risk of a breakage. But I do not have enough experience > with them to judge this. > > I can't remember any bug report in this code. I guess that only > few people use kmsg_dump. One of the problems doing that is that RCU and hung task detector, for example, have panic notifiers to disable themselves in the panic scenario - if we kmsg_dump() _before_ the panic notifiers, we may have intermixed messages, all messy...so for me it makes sense to keep the kmsg_dump() after panic notifiers. > [...] > Yes, panic_print_sys_info() increases the risk that the crash dump > will not succeed. But the change makes sense because: > > + panic_print_sys_info() does nothing by default. Most users will > not enable it together with crash dump. > > + Guilherme uses crash dump only to dump the kernel log. It might > be more reliable than kmsg_dump. In this case, panic_print_sys_info() > is the only way to get the extra information. > > + panic_print_sys_info() might be useful even with full crash dump. > For example, ftrace messages are not easy to read from the memory > dump. The last point is really good, I didn't consider that before but makes a lot of sense - we can now dump (a hopefully small!) ftrace/event trace buffer to dmesg before a kdump, making it pretty easy to read that later. Cheers, Guilherme _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
